Simulation of Fire Spread in Underground Cable Tunnel of Substation Under Different Ventilation Conditions

If the ventilation condition in the underground cable tunnel of the substation is not good, due to the heat emitted from long running cable, the temperature could be raised, and the carrying capacity of the cable could be reduced, sometimes resulting in cable combustion with considerable economic loss. When a fire occurs in the cable tunnel, tunnel ventilation not only takes away the heat generated by the burning of cables in the tunnel, but also increases the oxygen content in the tunnel, which has positive and negative effects on the spread of fire. Therefore, the selection of proper ventilation conditions is of great significance to the suppression of fire spread in the cable tunnel. The fire spreading in underground cable tunnel under different ventilation conditions was simulated in this paper. The model was divided into A and B zones by the firewall to simulate the cable fire situation when the fire blocking material failed on the fireproof wall. The height of firewall hole and cable diameter should be 0.08m, and the cable spacing should be 0.04m. The heat source was placed under the cable in zone A to simulate the situation when the cable in zone A fired and spread to zone B. Besides, a square vent with a side length of 1m was set above the two zones respectively, where the vent at the top of area A was used as the inlet, and the vent at the top of area B was used as the outlet. The wind speed of the two areas remained the same. The results showed that the closed environment was not conducive to the diffusion of the cable combustion products, and the combustion products were easy to accumulate in the fire area and had little influence on the adjacent area. With ventilation considered, the speed at which oxygen and carbon dioxide gas content reached the stable value again was shortened with the diffusion of flue gas to the adjacent region accelerated. Furthermore, the visibility inside the tunnel was also improved under ventilation conditions, resulting in the heat exchange between both the two zones and the outside environment accelerated. When the wind speed increased, the temperature of the cable tunnel in A and B regions tended to decrease.